The present invention relates to a 2-cyanoacrylate composition having excellent surface curability and clearance curability.
2-Cyanoacrylate compositions undergo instantaneous anionic polymerization to exhibit a high bonding strength. The compositions are hence widely utilized especially as instantaneous adhesives in various industrial fields.
However, it is not satisfactory to use the compositions as potting materials, fillers or instantaneous adhesives because the compositions necessitate a considerably prolonged setting time with respect to curability in a relatively wide gap between adherends (hereinafter referred to as xe2x80x9cclearance curabilityxe2x80x9d) or curability on a surface of an adherent due to overflowing the composition (hereinafter referred to as xe2x80x9csurface curabilityxe2x80x9d).
For overcoming the problem, various proposals have been made on the use of surface-treating agents which increase the curing rate of 2-cyanoacrylate compositions.
For example, JP-B-62-29471 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d) discloses a composition comprising an N,N-di(lower alkyl)toluidine, saccharin and ascorbic or isoascorbic acid, and JP-B-62-12279 discloses the use of a specific surfactant.
JP-B-60-24826 discloses the use of methylolurea which may have been partly alkoxylated, melamine, or a derivative of either. JP-B-54-19416 and JP-B-51-25441 disclose a technique in which an adherend is treated beforehand with N,N-dimethyl-m-toluidine and with a vinyl ether or vinyl thioether, respectively. JP-B-49-12094 discloses a technique in which an adherend surface is treated with a liquid containing an amine, amide or imide, and JP-B-48-44175 discloses a technique in which an adherend surface is treated with a liquid containing a specific heterocyclic compound. JP-B-47-8718 discloses a technique in which an adherend surface is treated beforehand with a liquid containing dimethylaniline or/and tris[1-(2-methyl)aziridiyl]phosphine oxide. Furthermore, JP-A-39-844 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses a technique in which an adherend surface is treated beforehand with an epoxide or diepoxide.
Curing accelerators to be added to 2-cyanoacrylate compositions have also been investigated in order to improve curability. For example, U.S. Pat. No. 4,171,416 discloses the use of a crown ether compound as a curing accelerator. U.S. Pat. Nos. 4,170,585 and 4,377,490 disclose the use of a polyalkylene glycol derivative having a specific structure and a mixture of an aliphatic or aromatic polyol with an aliphatic or aromatic polyether, respectively, as a curing accelerator. U.S. Pat. Nos. 4,386,193 and 5,589,554 disclose the use of a three- or four-arm polyol podand compound having a specific structure and a compound having cyano and carboxy groups, respectively, as a curing accelerator. Furthermore, JP-B-5-72946 and JP-A-7-316505 disclose the use of a calixarene compound and an organotitanium compound, respectively, as a curing accelerator.
It has further been attempted to improve surface curability and clearance curability by adding photocurability to a 2-cyanoacrylate composition. For example, JP-A-9-249708 discloses the use as an anionic photopolymerization initiator of a metallocene compound comprising a transition metal of Group VIII of the periodic table and aromatic electron system ligands. JP-A-6-299122 and International Publication WO 93/10483 disclose the use of an aromatic azide compound and an inorganic chromium complex, respectively, as an anionic photopolymerization initiator. Furthermore, JP-A-62-57475 discloses a cyanoacrylate-based adhesive composition containing a free-radical photopolymerization initiator.
However, the techniques described above each have had one or more disadvantages as will be described below, such as poor applicability, poor storage stability and the necessity of an illuminator. Namely, these techniques have been unsatisfactory because the advantage inherent in 2-cyanoacrylate compositions, that the operation can be completed in a short period of time, is lost.
The technique in which a surface-treating agent is used is satisfactory in attaining a shortened operation period because it greatly improves surface curability and clearance curability. However, applicability is considerably impaired because two liquids should be applied.
Although the technique in which a curing accelerator is used is effective in improving curability in application to closely spaced adherends, it has been unsatisfactory in surface curability and clearance curability.
The technique in which photocurability is added is satisfactory in operation period because it can improve surface curability and clearance curability. However, this technique has been unsatisfactory in that it necessitates a light irradiation device and that it is unusable for the bonding of adherends having such a structure that irradiation of the bonding surface with light is impossible.
Namely, there has been a desire since long before for a 2-cyanoacrylate composition which is usable as one component and curable at ambient temperature, and not necessitating a light irradiation device or the like and which cures in a short period of time even in the case where it is used as a potting material, or has overflowed, or is applied to a relatively wide gap between adherends.
The present invention has been made to overcome the above-described disadvantages in the conventional techniques.
Accordingly, an object of the present invention is to provide a 2-cyanoacrylate composition having excellent surface curability and clearance curability and being effective in shortening the time required for bonding operation.
As a result of intensive investigations to overcome the above-described conventional problems, it has been found that all the above-described problems are overcome and surface curability and clearance curability are greatly improved by containing a Lewis acid metal salt comprising a specific metal and a conjugate base comprising an acid having oxygen, and a compound having clathrating ability into a 2-cyanoacrylate. The present invention has been completed based on this finding.
The present invention provides a 2-cyanoacrylate composition comprising (1) a Lewis acid metal salt which comprises a metal selected from the group consisting of zinc, cadmium, mercury, aluminum, gallium, indium and thallium (hereinafter, the metal is referred to as xe2x80x9cspecific metalxe2x80x9d) and a conjugate base comprising an acid having oxygen, wherein the metal is bonded to the conjugate base through an oxygen atom, and (2) a compound having clathrating ability.
In connection with the incorporation of a Lewis acid metal salt into a 2-cyanoacrylate, JP-W-63-500247 (the term xe2x80x9cJP-Wxe2x80x9d as used herein means an xe2x80x9cunexamined published PCT applicationxe2x80x9d) discloses a technique in which a metal salt such as FeCl3 or CdCl2 is incorporated as an inhibitor into a 2-cyanoacrylate. However, those metal salts, in which the central atom is directly bonded to halogen atoms, have an exceedingly high acidity and are utterly different from the Lewis acid metal salt used in the present invention, which is intended to improve curing rate. Furthermore, JP-A-62-89780 discloses a technique in which an electroconductive powder of, e.g., silver, copper, nickel or aluminum is incorporated into a cyanoacrylate together with a basic substance such as a crown ether. However, those metals used in this technique are solid and remain undissolved in the cyanoacrylate. This technique therefore is utterly different from the invention, in which the metal salt used is soluble in cyanoacrylates.